Image farming and microdevice manufacturing method and exposure apparatus in which a light source includes four quadrants of predetermined intensity

ABSTRACT

An exposure apparatus for and a method of forming an image of a fine pattern having linear features extending in orthogonal first and second directions. The apparatus includes an illumination optical system for illuminating the pattern. The illumination optical system includes a device for forming a secondary light source having decreased intensity portions at a center thereof and on first and second intersecting axes defined along the first and second directions, respectively. A projection optical system projects, on an image plane, an image of the pattern illuminated with light from the light source. The light source includes four sections having substantially the same intensity and being distributed in the four quadrants defined by the axes. An image of the light source is projected onto a pupil of the projection optical system. On the assumption of a coordinate system defined X and Y-axes extending along the first and second directions and intersecting at a center of the pupil, and that a radius of the pupil is one, coordinates of centers of the four sections are (p, p), (-p, p), (-p, -p) and (p, -p), wherein 0.25&lt;p&lt;0.6.

This application is a divisional of application, Ser. No. 08/427,709filed Apr. 24, 1995, which application is a continuation of priorapplication, Ser. No. 08/357,786 filed Dec. 16, 1994, which applicationis a continuation of prior application, Ser. No. 08/270,414 filed Jul.5, 1994, which application is a continuation of prior application, Ser.No. 08/159,954 filed Dec. 1, 1993, which application is a continuationof prior application, Ser. No. 08/065,498 filed May 24, 1993, all nowabandoned, which application is a divisional of prior application, Ser.No. 07/836,509 filed Feb. 18, 1992 now U.S. Pat. No. 5,305,054.

FIELD OF THE INVENTION AND RELATED ART

This invention relates generally to an imaging method for manufacture ofmicrodevices. More particularly, in one aspect the invention isconcerned with an imaging method or an illumination method therefor,suitably usable in forming on a workpiece a fine pattern of a linewidthof 0.5 micron or less.

The increase in the degree of integration of a semiconductor device hasbeen accelerated more and more and, along such a trend, the fineprocessing techniques have been improved considerably. Particularly, theoptical processing technique which is a major one of them has beenadvanced to a level of submicron region, with the start of a 1 megaDRAM. A representative optical processing machine is a reductionprojection exposure apparatus, called a "stepper". It is not too much tosay that enhancement of resolution of this apparatus determines thefuture of the semiconductor device.

Conventionally, the enhancement of resolution of the stepper mainlyrelies on enlarging the N.A. (numerical aperture) of an optical system(reduction projection lens system). Since however the depth of focus ofan optical system is in inverse proportion to the square of the N.A.,the enlargement of the N.A. causes an inconvenience of decreased depthof focus. In consideration of this, attempts have been made recently tochange the wavelength of light for exposure, from the g-line to thei-line or to excimer laser light of a wavelength not longer than 300 nm.This aims at an effect that the depth of focus and the resolution of anoptical system can be improved in inverse proportion to the wavelength.

On the other hand, in a way separate from shortening the exposurewavelength, a method using a phase shift mask has been proposed as ameasure for improving the resolution. According to this method, a thinfilm is formed in a portion of a light transmitting area of a mask,which film serves to provide a phase shift of 180 deg. with respect tothe other portion. The resolution RP of a stepper can be represented byan equation RP=k₁ λ/N.A., and usually the stepper has a k₁ factor of alevel of 0.7-0.8. With the method using such a phase shift mask, thelevel of the k₁ factor can be improved to about 0.35.

However, there remain many problems to realize such a phase shift maskmethod. Unsolved problems currently remaining are such as follows:

(1) A satisfactory thin film forming technique for forming a phase shiftfilm has not yet been established.

(2) A satisfactory CAD (computer-aided designing) for design of acircuit pattern with a phase shift film has not yet developed.

(3) Depending on a pattern, a phase shift film cannot be appliedthereto.

(4) With respect to the inspection and correction of a phase shift film,a satisfactory technique has nut yet been established.

As stated, there remain many problems to realize a phase shift maskmethod.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a unique andimproved imaging method suitable for manufacture of microdevices such assemiconductor microcircuit devices.

It is another object of the present invention to provide a microdevicemanufacturing method which uses such an imaging method.

It is a further object of the present invention to provide an exposureapparatus for manufacture of microdevices, which uses such an imagingmethod.

In accordance with a first aspect of the present invention, there isprovided an imaging method for imaging a fine pattern having linearfeatures extending along orthogonal first and second directions,characterized by: providing a light source having decreased intensityportions at a center thereof and on first and second axes defined tointersect with each other at the center and defined along the first andsecond directions, respectively; end illuminating the pattern with lightfrom the light source.

In accordance with a second aspect of the present invention, there isprovided a method of imaging a fine pattern having linear featuresextending in orthogonal first and second directions, wherein the patternis illuminated with light obliquely with respect to the pattern, theimprovements residing in that: the strength of illumination in apredetermined plane of incidence is made greater than that in a firstplane of incidence including the first direction and that in a secondplane of incidence including the second direction and intersecting withthe first plane of incidence perpendicularly.

In accordance with a third aspect of the present invention, there isprovided a method of imaging a fine pattern having linear features eachextending in a predetermined direction, wherein the pattern isilluminated with light obliquely with respect to the pattern, theimprovements residing in that: the illumination of the pattern withlight along a path in a plane of incidence including the predetermineddirection is substantially blocked; and the pattern is illuminated withlight along a pair of paths which are symmetrical with each other withrespect to the plane of incidence.

In accordance with a fourth aspect of the present invention, there isprovided an illumination method in image projection, for illuminating afine pattern of an original, characterized by: providing a lightintensity distribution having decreased intensity portions eta centerthereof and on first and second orthogonal axes with respect to whichthe original is to be placed.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for explaining the principle of projection ofan image of a fine pattern.

FIGS. 2A and 2B are schematic views, respectively, wherein FIG. 2A showsa light distribution as provided on a pupil by diffraction light from aconventional mask and FIG. 2B shows a light distribution as provided ona pupil by diffraction light from a phase shift mask.

FIGS. 3A and 3B show a first embodiment of the present invention,wherein FIG. 3A is a schematic view of an example of an effective lightsource as formed on a pupil by zero-th order light in the firstembodiment and FIG. 3B shows another example of an effective lightsource as formed on a pupil by zero-th order light in the firstembodiment.

FIG. 4 is a graph for explaining frequency characteristics of aprojection system which forms the effective light source of the FIG. 3Aexample and that of a projection system of conventional type.

FIGS. 5A-5C show a second embodiment of the present invention, whereinFIG. 5A is a schematic view of a projection exposure apparatus accordingto the second embodiment of the present invention, FIG. 5B is a frontview of a stop member used in the second embodiment, and FIG. 5C is aschematic view of a cross filter used in the second embodiment.

FIGS. 6A and 6B show a third embodiment of the present invention,wherein FIG. 6A is a schematic view of a project, on exposure apparatusaccording to the third embodiment and FIG. 6B is a front view of a stopmember used in the third embodiment.

FIG. 7 is a fragmentary schematic view of a projection exposureapparatus according to a fourth embodiment of the present invention.

FIG. 8 is a fragmentary schematic view of a projection exposureapparatus according to a fifth embodiment of the present invention.

FIG. 9 is a fragmentary schematic view of a projection exposureapparatus according to a sixth embodiment of the present invention.

FIG. 10 is a fragmentary schematic view of a projection exposureapparatus according to a seventh embodiment of the present invention.

FIG. 11 is a fragmentary schematic view of a projection exposureapparatus according to an eighth embodiment of the present invention.

FIG. 12 is a fragmentary schematic view of a projection exposureapparatus according to a ninth embodiment of the present invention.

FIG. 13 is a schematic view of a main portion of a projection exposureapparatus according to a tenth embodiment of the present invention.

FIG. 14 is a schematic view for explaining the relationship between apupil of a projection optical system and an optical integrator.

FIGS. 15A and 15B are schematic views, respectively, each showing thepupil of the projection optical system.

FIG. 16 is a schematic view of a stop member usable in the presentinvention.

FIGS. 17A and 17B are schematic views, respectively, each showing themanner of cabling a mercury lamp.

FIG. 18 is a schematic view of a main portion of a projection exposureapparatus according to a further embodiment of the present invention.

FIGS. 19A and 19B are schematic views, respectively, for explaining themanner of insertion of a pyramid type prism used in another embodimentof the present invention.

FIG. 20 is a schematic view of a main portion of a projection exposureapparatus according to a still further embodiment of the presentinvention.

FIG. 21 is a schematic view of a main portion of a projection exposureapparatus according to a still further embodiment of the presentinvention.

FIG. 22 is a schematic view of a main portion of a projection exposureapparatus according to yet a further embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For better understanding of the present invention, description will bemade first on details of the imaging of a fine pattern.

FIG. 1 shows the principle of image projection of a fine pattern 6having a high frequency (pitch 2d is about several microns), through aprojection lens system 7. The fine pattern 6, which is illuminated alonga direction perpendicular to the surface thereof, diffracts the lightinputted thereto. Diffraction lights caused thereby include a zero-thorder diffraction light, directed in the same direction as the directionof advancement of the input light, and higher order diffraction lightssuch as positive and negative first order diffraction lights, forexample, directed in directions different from the input light. Amongthese diffraction lights, those of particular diffraction orders suchas, for example, the zero-th order diffraction light and positive andnegative first order diffraction light, are incident on a pupil 1 of theprojection lens system 7. Then, after passing through the pupil 1, theselights are directed to an image plane of the projection lens system,whereby an image of the fine pattern 6 is formed on the image plane. Inthis type of image formation, the light components which arecontributable to the contrast of the image are higher order diffractionlights. If the frequency of a fine pattern increases, it raises aproblem that an optical system does not receive higher order diffractionlights. Therefore, the contrast of the image degrades and, ultimately,the imaging itself becomes unattainable.

FIG. 2A shows a light distribution on the pupil 1 on an occasion whenthe fine pattern 6 of FIG. 1 is formed on a mask of conventional type,while FIG. 2B shows a light distribution on the pupil 1 on an occasionwhen the fine pattern 6 is formed on a phase shift mask.

In FIG. 2A, about a zero-th order diffraction light 3a, there are apositive first order diffraction light 3b and negative first orderdiffraction light 3c. In FIG. 2B, on the other hand, due to the effectof a phase shift film a zero-th order diffraction light 5a is"extinguished" and there are positive and negative first orderdiffraction lights 5b and 5c only. Comparing the cases of FIGS. 2A and2B, the following two points may be raised as advantageous effects of aphase shift mask upon the plane of spatial frequency, i.e., the pupilplane:

(1) In the phase shift mask, the frequency is decreased to a half.

(2) In the phase shift mask, no zero-th order diffraction light exists.

Another point to be noted here may be that the spacing a between thepositive and negative first order diffraction lights upon the pupilplane in the case of the phase shift mask corresponds to the spacing abetween the zero-th order light and the positive (negative) first orderdiffraction light in the case of the conventional type mask.

On the other hand, as regards the light distribution on the pupil 1, theconventional type mask and the phase shift type mask show the samecharacteristic with respect to the position. What is the differencetherebetween is the ratio of intensity of the amplitude distributionupon the pupil 1. In the phase shift mask shown in FIG. 2B, theamplitude ratio among the zero-th order, positive first order andnegative first order diffraction lights is 0:1:1, whereas in theconventional type mask shown in FIG. 2A it is 1:2/π:2/π.

In accordance with one aspect of the present invention, a lightdistribution similar to that to be produced by a phase shift type maskcan be produced on the pupil 1. More specifically, according to thisaspect of the present invention, in order to assure that, when a finepattern 6 (more particularly, a fine pattern as having a spatialfrequency that the k₁ factor is about 0.5, as suggested in theintroductory part of the Specification) is illuminated, a zero-th orderdiffraction light is incident on the pupil 1 at a position off thecenter of the pupil 1 while a different diffraction light of higherorder is similarly incident on a position off the center of the pupil 1,an optical arrangement is provided to produce such an effective lightsource that: it has a light quantity distribution in which, as comparedwith the light intensity in each of portions on a pair of axis passingthrough the center of the pupil and extending along longitudinal andlateral pattern features of the fine pattern and as compared with thelight intensity in a portion around the center of the pupil, the lightintensity in a portion other than these portions is higher. Preferably,there may be produced an effective light source in which the lightintensity at each of the portions on the pair of axes passing throughthe center of the pupil and extending along the longitudinal and lateralpattern features of the fine pattern as well as the light intensity inthe portion around the center of the pupil, are lowered to about zero.

When such an effective light source is provided, of zero-th order andfirst order diffraction lights, for example (as produced as a result ofillumination of a fine pattern of a k₁ factor of about 0.5, forexample), the zero-th order diffraction light and one of the positiveand negative first order diffraction lights may be projected on thepupil 1 whereas the other of the positive and negative first orderdiffraction lights may be prevented from being projected onto thepupil 1. This assures a light distribution similar to that to beprovided by a phase shift mask on the pupil 1.

If in the present invention a single light beam is used for theillumination, the amplitude ratio of a pair of diffraction lights at thepupil 1 becomes 1:2/π, different from a desirable amplitude ratio of 1:1similar to what as attainable with a phase shift mask. However,according to the analyses made by the inventors of the subjectapplication, it has been found that: for resolving a longitudinalpattern feature of a mask, such a difference in amplitude ratio can besubstantially compensated by using, as the light to be obliquelyprojected on the mask (fine pattern), a pair of lights from a pair oflight sources disposed symmetrically with each other with respect to alongitudinal axis of the pupil (an axis passing through the center ofthe pupil and extending along the longitudinal pattern feature) so as toproduce on the pupil a pair of light patterns which are symmetrical witheach other with respect to the longitudinal axis of the pupil; and thatfor resolving a lateral pattern feature of the mask, the difference inamplitude ratio can be compensated by using, as the light to beprojected obliquely on the mask (fine pattern), a pair of lights from apair of light sources disposed symmetrically with each other withrespect to a lateral axis of the pupil (an axis passing through thecanter of the pupil, extending along the lateral pattern feature andbeing perpendicular to the longitudinal axis of the pupil) so as toproduce a pair of light patterns which are symmetrical with each otherwith respect to the lateral axis of the pupil.

For resolving a mask pattern having longitudinal and lateral patternfeatures, two illumination light beams, for example, may be used andprotected obliquely to the mask so as to produce an effective lightsource having, on the pupil, a light quantity distribution with a pairof peaks of substantially the same intensity at those positions: whichare symmetrical with each other with respect to the center of the pupil,and which are located along a first axis passing through the center ofthe pupil and extending with an angle of about 45 deg. with respect tothe X and Y axes. Also, four illumination light beams, for example, maybe used and projected obliquely to the mask so as to produce aneffective light source having, on the pupil, a light quantitydistribution with (1) a pair of portions of substantially the sameintensity at those positions: which are symmetrical with each other withrespect to the center of the pupil, and which are located along a firstaxis passing through the center of the pupil and extending with an angleof about 45 deg. with respect to the X and Y axes and (ii) with a pairof portions of substantially the same intensity at those positions:which are symmetrical with each other with respect to the center of thepupil, which are located along a second axis passing through the centerof the pupil and extending with an angle of about 90 deg. with respectto the first axis, and which are at substantially correspondinglocations with respect to the pair of positions on the first axis andthe center of the pupil.

A first embodiment of the present invention will be explained withreference to FIGS. 3A and 3B, wherein FIG. 3A shows a light distributionof zero-th order diffraction light on the pupil 1 of FIG. 1, while FIG.3B shows a distribution of an effective light source on a pupil plane.

In the drawings, denoted at 1 is a pupil; denoted at x is a lateral axisof the pupil (an axis passing through the center of the pupil andextending along a lateral pattern feature); denoted at y is alongitudinal axis of the pupil (an axis passing through the center ofthe pupil, extending along a longitudinal pattern feature and beingperpendicular to the x axis); and denoted at 2a, 2b, 2c and 2d areportions of an effective light source.

In these two examples, the effective light source has a distributiongenerally consisting of four portions. Each portion (light pattern) hasa distribution of circular shape. If the radius of the pupil 1 is 1.0,the pupil center is at the origin of the coordinate and the x and y axesare the orthogonal coordinate axes, then in the FIG. 3A example thecenters of the portions 2a, 2b, 2c and 2d are at the positions (0.45,0.45), (-0.45, 0.45), (-0.45, -0.45) and (0.45, -0.45), and the radiusof each portion is 0.2. In The FIG. 3B example, the centers of theportions 2a, 2b, 2c and 2d are at the positions (0.34, 0.34), (-0.34,0.34), (-0.34, -0.34) and (0.34, -0.34), and the radius of each portionis 0.25.

The effective light source according to this embodiment is characterizedin that: when the pupil plane is divided into four quadrants by the xand y axes defined on the pupil plane, as stated above, each portion 2a,2b, 2c or 2d is defined in corresponding one of the quadrants and alsothese portions are defined in a symmetrical relationship and definedindependently of each other, without overlapping. Here, the x and y axesfor the division of the quadrants correspond to the x and y axes, forexample, used for the design of an integrated circuit pattern and theycorrespond to the directions of elongation of longitudinal and lateralpattern features of a mask.

The shape of the effective light source according to this embodiment isdetermined in specific consideration of the directivity of longitudinaland lateral pattern features of a fine pattern whose image is to beprojected, and it is characterized In that: the centers of the fourcircular portions 2a-2d are just on ±45 deg. directions (the directionsalong a pair of axes passing through the center of the pupil 1 andextending with angles of ±45 deg. with respect to the x and y axes). Inorder to produce such an effective light source, a light source(secondary light source) having the same shape and the samerelationship, with respect to the x and y axes, as that illustrated maybe provided on a plane optically conjugate with the pupil 1 and fourillumination light beams from the provided light source may be projectedobliquely to a fine pattern at the same angle of incidence and along twoorthogonal planes of incidence (each two light beams in a pair). Thisassures that: linear pattern features extending along the x axis areilluminated obliquely by the light beams projected along the paths whichare symmetrical with each other with respect to the plane of incidenceincluding the x axis; while linear pattern features extending along they axis are illuminated obliquely by the light beams projected along thepaths which are symmetrical with each other with respect to the plane ofincidence including the y axis.

It is important that the four portions 2a-2d of The effective lightsource have substantially the same intensity. If the intensity ratiochanges, any defocus of a wafer during the printing thereof, forexample, causes deformation of the image of a circuit pattern. For thisreason, preferably the four illumination light beams are so set as toprovide the same intensity. As regards the intensity distribution ofeach of the four portions 2a-2d, it may be determined as desired. Forexample, it may be a uniform intensity distribution wherein the wholerange is at a peak level, or it may be a non-uniform intensitydistribution wherein the peak is only at the center. This means that thefour illumination light beams may take various forms in accordance withthe form of an effective light source to be provided on the pupil 1. Asan example, while in this embodiment the four portions of the effectivelight source are separated from each other and thus no light pattern isproduced in a portion other than the four portions, the four portions ofthe effective light source may be formed to be continuous with theintervention of lower intensity light patterns.

The distribution (shape) of each of the four portions 2a-2d of theeffective light source is not limited to a circular shape. However, itis desirable that, independently of the shape, the centers of the fourportions or the gravity centers of their intensity distributions are ina symmetrical relationship and are on the ±45 deg. directions withrespect to the x and y axes, as in the examples of FIGS. 3A and 3B.

For further enhancement of resolution, i.e., in an attempt to adopt anarrangement of an optimum effective light source adapted to provide asystem of lower k₁ level, it is seen from the comparison of FIG. 3A withFIG. 3B that the gravity center position of each portion 2a, 2b, 2c or2d of the effective light source in each quadrant displaces away fromthe center of the pupil 1 and, as a result, the diameter of eachindependent portion 2a, 2b, 2c or 2d in a corresponding quadrantdecreases.

Illustrated in FIGS. 3A and 3B are two types of effective light sourcesexpected. In a practical design, an effective light source similar tothese two types may be used, since, if the gravity center position ofeach portion of the effective light source is too far from the center ofthe pupil 1, a problem of a decrease of light quantity, for example, mayresult (in the respect of convenience in design of the optical system).

According to the investigations on that point made by the inventors, ithas been found that: in the coordinate and the pupil 1 shown in FIGS. 3Aand 3B, if each of a pair of portions 2a and 2c which are in the firstand third quadrants, respectively, and which are spaced from each otherhas a circular shape and a radius q and if the center positions (gravitycenter positions) of the first and second portions 2a and 2c are atcoordinates (p, p) and (-p, -p), respectively, then good results areobtainable by satisfying the following conditions:

0.25<p<0.6

0.15<q<0.3

It is to be noted that the size and position of each of the remainingportions 2b and 2d in the second and fourth quadrants are determinednaturally from the symmetry of them to the portions 2a and 2c in thefirst and third quadrants. Also, it has been found that, even in a casewhen each portion of the effective light source has a shape other than acircular shape, such as, for example triangular or rectangular,preferably the above conditions should be satisfied. In such a case, theradius of a circle circumscribing each portion may be used as the valueof q. In the examples shown in FIGS. 3A and 3B, each quantity is nearthe middle of the range defined by the corresponding condition. Thequantities of p and q may change depending upon a desired linewidth of afine pattern which is required to be projected by the optical system(illumination system/projection system) used.

In a currently used stepper, an effective light source has a peak at acenter (x, y)=(0, 0) of a pupil 1. In this type of apparatus, it is saidthat the coherence factor (σ level) is 0.3 or 0.5, and this means thatit has an effective light source distribution having a radius of 0.3 or0.5 about the center of the pupil 1. According to the analyses made bythe inventors, it has been found that: if an effective light source ispositioned close to the pupil center, for example, if the σ level is ina range not greater than 0.1, it provides an advantage that when defocusoccurs a high contrast can be retained mainly with regard to arelatively wide linewidth (a linewidth to which the above-described k₁factor is not less than 1). However, such an advantage as obtainablewhen defocus occurs diminishes quickly as the k₁ factor becomes close to0.5. If the k₁ factor goes beyond 0.5, in a strict case the contrast ofan image is lost fully. What is most required currently is theimprovement in defocus performance at a k₁ factor level not greater than0.6 and, in cases where the k₁ factor is at about this level, thepresence of an effective light source adjacent to the pupil center hasan adverse effect on the imaging.

As compared therewith, the effective light source having been describedwith reference to the first embodiment has a small k₁ factor. For Theimaging with respect to a k₁ factor of about 0.5, it provides anadvantageous effect of retaining a high contrast when defocus occurs.Since in the example of FIG. 3A each of the portions 2a-2d of theeffective light source is located outwardly, as compared with those ofthe FIG. 3B example, it provides a superior high frequencycharacteristic as compared with the FIG. 3B example. It is to be notedthat, in a portion of the effective light source spaced away from thepupil center, the defocus characteristic is such that, up to a k₁ factorof about 1, the depth of focus is maintained substantially at a constantlevel.

FIG. 4 shows the relationship between the resolution and the depth offocus in a case when the example of FIG. 3B is applied to an i-linestepper having a N.A. of 0.5, the calculations having been made on anassumption that the defocus in a range satisfying the contrast of anoptical image of 70% is within the depth of focus (tolerance). Curve Ain the drawing depicts the relationship between the resolution and thedepth of focus in the case of the conventional method (σ=0.5) using aconventional reticle, while curve B depicts the relationship between theresolution and the depth of focus in the case of the FIG. 3B example. Ifthe limit of the depth of focus of a stepper which may be practicallyadmitted is set to be equal to 1.5 micron, then the limit of resolutionis 0.52 micron in the case of the conventional method. As compared, inthe case of the FIG. 3B example, the resolution is improved to about 0.4micron. This corresponds to an improvement of about 30% in terms ofratio, which is considerably large in the field to which the presentinvention pertains. In effect, a resolution of about 0.45 (k₁ factor) iseasily attainable.

The present invention in this aspect differs from what can be called a"ring illumination method" wherein no effective light source is formedat the pupil center, in that: on the pupil 1, the effective light sourcehas a peak neither on the x axis nor on the y axis corresponding to thedirection of the longitudinal pattern feature or the lateral patternfeature of the fine pattern. This is for the reason that, if theeffective light source has a peak on the x axis or the y axis, thecontrast of an image degrades largely and thus a large depth of focus isnot obtainable. It has been confirmed that, with respect to the imageprojection of a fine pattern mainly consisting of longitudinal andlateral pattern features, the present invention assures formation of animage of improved image qualify as compared with that obtainable by thering illumination method.

The light quantity (light intensity) in each principal portion of theeffective light source of the present invention may be either uniform ornon-uniform such as a Gaussian distribution.

FIGS. 5A, 5B and 5C show a second embodiment of the present inventionand illustrate a semiconductor device manufacturing exposure apparatusarranged to project an image of a fine pattern in accordance with anaspect of the invention.

Denoted in the drawings at 11 is an ultra-high pressure Hg lamp havingits light emitting portion disposed at a first focal point of anelliptical mirror 12: denoted at 14, 21, 25 and 27 are deflectingmirrors: and denoted at 15 is an exposure control shutter. Denoted at105 is a field lens; denoted at 16 is a wavelength selectinginterference filter: denoted at 17 is a cross ND (neutral density)filter; denoted at 18 is a stop member having a predetermined aperture;denoted at 19 is an optical integrator having its light receivingsurface disposed at a second focal point of the elliptical mirror 12;and denoted at 20 and 22 are lenses of a first imaging lens system (20,22). Denoted at 23 is a half mirror; denoted at 24 is a masking bladedevice having a rectangular aperture for defining a region ofillumination on a reticle; denoted at 26 and 28 are lenses of a secondimaging lens system (26, 28); and denoted at 30 is a reticle havingformed thereon an integrated circuit pattern mainly consisting oflongitudinal and lateral pattern features (grid-like linear features) ofa minimum linewidth of about 2 microns. Denoted at 31 is a reductionprojection lens system for projecting the circuit pattern of the reticle30 in a reduced scale of 1:5; denoted at 32 is a wafer coated with aresist; denoted at 33 is a wafer chuck for holding the wafer 32 byattraction: and denoted at 34 is an X-Y stage for supporting the waferchuck 33 and being movable in x and y directions of an X-Y coordinatesystem defined in the exposure apparatus in relation to the X-Y stage.Denoted at 35 is a glass plate having formed thereon a light blockingfilm with an aperture 35a at its center: denoted at 36 is a casinghaving an aperture formed in its top surface: denoted at 37 is aphotoelectric converter provided in the casing 36; and denoted at 38 isa mirror which is a component of a laser interferometer (not shown) formeasuring the amount of movement (x axis) of the wafer stage 34. Denotedat 40 is a light blocking plate having a predetermined aperture, whichis disposed at a position optically equivalent to the light receivingsurface of the blade 24 so that, like the blade 24, the light beamsemanating from the lenses of the optical integrator 19 are overlappedone upon another on the plate 40. Denoted at 41 is a condensing lens forcollecting light passed through the aperture of the light blocking plate40; and denoted at 42 is a quartered detector.

As is well known in the art, usually a circuit pattern of a reticle(mask) is designed with reference to orthogonal axes (coordinates) sothat longitudinal pattern features and lateral pattern features of thepattern extend along these axes, respectively. When such a reticle isintroduced into a projection exposure apparatus, the reticle is placedon a reticle stage with reference to x and y axes of an X-Y coordinatesystem defined in the exposure apparatus, with the orthogonal designaxes of the reticle placed exactly or substantially aligned with the xand y axes of the exposure apparatus. Also, the the X-Y stage on which awafer is placed has an X-Y coordinate system with x and y axes alongwhich the X-Y stage is movable. These x and y axes of the X-Y stage aredesigned to exactly or substantially correspond to the x and y axes ofthe exposure apparatus. Thus, when a reticle is placed in the exposureapparatus, usually the directions of longitudinal and lateral patternfeatures of the reticle are placed in exactly or substantially exactlyalignment with the x and y axes defined in the exposure apparatus,respectively, or with the x and y axes along which the X-Y stage moves.

A structural feature of this apparatus resides in the filter 17 and thestop member 18 disposed in front of the integrator 19. As shown in FIG.5B, the stop member 18 comprises an aperture stop with a ring-likeaperture, for blocking the light near the optical axis of the apparatus,and it serves to define the size and shape of an effective light sourceon the pupil plane of the projection lens system 31. The center of theaperture is aligned with the optical axis of the apparatus. On the otherhand, as shown in FIG. 5C, the filter 17 comprises four ND filters whichare disposed, as a whole, in a cross-like shape. These four ND filtersserve to attenuate the intensity of light, projected to four zones inthe ring-like aperture of the stop member 18, by 10-100%. These fourzones correspond respectively to the portions on the pupil plane of theprojection lens system 31, which portions include four points on the xand y axes corresponding respectively to the directions of thelongitudinal and lateral pattern features of the reticle 30. By means ofthis filter 17, the light intensity at the central portion of asecondary light source as formed at the light emitting surface of theintegrator 19 as well as the light intensity along the x and y axes,intersecting with each other at the center of the secondary lightsource, are attenuated and, as a result, the light intensity of theeffective light source along the x and y axes on the pupil plane of theprojection lens system 31 is attenuated.

The reticle 30 is held on a reticle stage, not shown. The projectionlens system 31 may be designed with respect to light of i-line(wavelength 365 nm) as selected by the filter 16. The first and secondimaging lens systems (20, 22, 26, 28) are so set as to place the lightemitting surface of the integrator 19 and the pupil plane of theprojection lens system 31 in an optically conjugate relationship, whilethe second imaging lens system (26, 28) is so set as to place the edgeof the aperture of the blade device 24 and the circuit pattern of thereticle 30 in an optically conjugate relationship. The blade device 24comprises four light blocking plates each having a knife-edge like endand each being movable independently of the others so as to allowadjustment of the size of the aperture in accordance with the size ofthe integrated circuit pattern on the reticle 30. The position of eachlight blocking plate is controlled in response to a signal from acomputer (not shown) provided for the overall control of the apparatus,and the size of the aperture is optimized to the reticle 30 used. Whilenot shown in the drawings, the exposure apparatus is equipped with areticle alignment scope to be used for aligning the reticle 30 withrespect to the exposure apparatus as well as an off-axis alignment scopedisposed beside the projection lens system 31, for aligning the wafer 32with respect to the reticle 30.

The half mirror 23 serves to reflect a portion of light from theintegrator 19, and the reflected light is projected through the apertureof the light blocking plate 40 and is collected by the condensing lens41 upon the quartered detector 42. The detector 42 has a light receivingsurface disposed to be optically equivalent to the pupil plane of theprojection lens system 31, and a ring-like effective light source asformed by the stop member 18 is projected on this light receivingsurface. Each detector section of The detector 42 produces a signalcorresponding to the intensity of light impinging on the surface of thatsection. By integrating The output signals of the sections of thedetector 42, an integration signal for the opening/closing control ofthe shutter 15 is obtainable.

The components 35-37 disposed on the X-Y stage 34 provide a measuringunit for examination of the performance of the illumination system abovethe reticle 30. For the examination of the illumination system, the X-Ystage 34 moves to a predetermined position to place the measuring unitat a position just below the projection lens system 31. In thismeasuring unit, light emanating from the illumination system andreaching the image plane of the projection lens system 31 is directedthrough the aperture 35a of the glass plate 35 and the aperture of thecasing 36 to the photoelectric converter 37. The light receiving planeof the aperture 35a is placed at the image plane position of theprojection lens system 31 and, if necessary, by using an unshown focusdetecting system (a sensor of well known type, for detecting the levelof the wafer 32 surface) as well as a measuring unit provided in the X-Ystage 34, the level of the aperture 35a in the direction of the opticalaxis of the apparatus may be adjusted. The glass plate 35 is attached tothe casing 36, and the casing 36 has formed therein an aperture asdescribed. In this example, the measuring unit is so arranged that theaperture of the casing 36 is displaceable to the aperture of the glassplate by a predetermined amount. The aperture of the casing 36 is placedat such a location at which the N.A. at the image plane side of theprojection lens system 31 is large and also which is spaced sufficientlyfrom the image plane. As a result, at the light receiving plane of theaperture of the casing 36, the same light distribution as provided onthe pupil plane of the projection lens system 31 is produced. In thisembodiment, such a measuring unit is not used. How the measuring unit isto be used will be described later with reference to an embodiment to bedescribed hereinafter.

In this embodiment: through the function the filter 17 and the stopmember 18, an effective light source having a generally ring-like shapebut having decreased intensity portions, including four zones on the xand y axes corresponding to the directions of the longitudinal andlateral pattern features of the reticle 30, as compared with theintensity of the other portions, is defined on the pupil plane of theprojection lens system 31; by means of the illumination system (11, 12,14, 15, 105, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 and 28), thecircuit pattern of the reticle 30 is illuminated with uniformilluminance; and an image of the circuit pattern is projected by theprojection lens system 31 upon the wafer 32, whereby the image of thecircuit pattern is transferred (printed) onto the resist of the wafer32. The effect of such projection exposure is as has been describedhereinbefore and, with light of i-line, a fine pattern of 0.4 micron canbe recorded on the resist of the wafer 32 sharply and stably.

While in this example the filter 17 and the stop member 18 are disposedin front of the integrator 19, they may be disposed just after theintegrator, particularly at a location which is optically conjugate withthe pupil plane of the projection lens system 31. Further, a stop member18 which is shown in FIG. 6B and is used in a third embodiment, to bedescribed later, may be used in substitution for the filter 17 and thestop member 18.

FIGS. 6A and 6B show a third embodiment of the present invention whichis another example of a semiconductor device manufacturing projectionexposure apparatus wherein an image of a fine pattern is projected inaccordance with a method of the present invention.

In the drawings, corresponding elements or those elements havingcorresponding functions as those in FIGS. 5A-5C, are denoted by the samereference numerals. Comparing the apparatus of this embodiment with thatof FIGS. 5A-5C, the former differs from the latter in that: as shown inFIG. 6B, the aperture of the stop member 18 comprises four separateapertures; in place of the cross ND filter, four separate filters 17a,17b, 17c and 17d corresponding respectively to the separate apertures ofthe stop member 18 are used; and a pyramid-like prism 13 is insertedbetween the mirrors 12 and 14.

In this embodiment, the output of the quartered detector 42 is used notonly for the opening/closing control of the shutter 15 but also for adifferent purpose or purposes. Additionally, the measuring unit (35-37)is used.

Now, referring mainly to the differences of the present embodiment tothe preceding embodiments, advantageous features of the presentembodiment will be explained.

If the integrator 19 is illuminated with light from the Hg lamp 11,without using the prism 13, the filters 17a-17d and the stop member 18,then a secondary light source having a light quantity distribution, likea Gaussian distribution, with a high peak at its center is formed on thelight exit surface of the integrator 19. Since the light exit surface ofthe integrator is optically conjugate with the pupil plane of theprojection lens system 31, an effective light source having a peak oflight quantity distribution, at the center of the pupil, is formed onthis pupil plane. As described hereinbefore, the effective light sourceto be used in this aspect of the present invention is one as having alight quantity distribution with no peak at the pupil center and,therefore, it is necessary to block the light impinging on a portionabout the center of the integrator 19. If, however, the stop member 18disposed simply in front of the integrator 19, a large portion of thelight from the Hg lamp is intercepted and thus the loss of lightquantity is large. In consideration thereof, in the present embodimentthe pyramid-like prism 13 is interposed just after the elliptical mirror12 to control the illuminance distribution on the optical integrator 19.

The Hg lamp 11 is so disposed that its light emitting portion coincideswith the first focal point position of the elliptical mirror 12, and thelight emanating from the Hg lamp 11 and reflected by the ellipticalmirror 12 is transformed by the prism 13 into four light beams deflectedin different directions. These four light beams are reflected by themirror 14 and reach the position of the shutter 15. If the shutter 15 isopen, the light beams are incident on the filter 16. By this filter 16,the i-line component is selected out of the emitted light spectrums ofthe Hg lamp 11, for ensuring the best performance of the projection lenssystem 31 for the projection of an image of the reticle 31 on a resist(photosensitive layer) of the wafer 32.

The four light beams from the filter 16 pass through the field lens 105and then impinge on the filters 17a-17d, respectively, which areimportant components of this embodiment. These four filters serve as acorrecting means for making the light quantities of the four light beamssubstantially uniform to thereby correct the symmetry in light quantityof four portions of the effective light source as formed on the lightexit surface of the integrator 19 and thus that as formed on the pupilplane of the projection lens system 31. If adjustment of the lightquantity attenuating function of each filter is desired, different typesof ND filters may be prepared for each filter so that they may be usedselectively. Alternatively, each filter may be provided by aninterference filter and, by utilizing the band narrowness of theinterference filter, the interference filter may be tilted to effect theadjustment.

The stop member 18 receives the four light beams from the filters17a-17d. As shown in FIG. 6B, the stop member 18 has four circularapertures which correspond to the four light beams from the filters17a-17d, in a one-to-one relationship. Thus, the integrator 19 isilluminated with four light beams from the four apertures of the stopmember 18, whereby an effective light source such as shown in FIG. 3Aand corresponding to the apertures of the stop member 18, is formed onthe light exit surface of the integral or 19 and thus on the pupil planeof the projection lens system 31.

Usually, the apertures of the stop member 18 each may have a shapecorresponding the outer configuration of each of small lensesconstituting the integrator 19. If, therefore, each small lens of theintegrator has a hexagonal sectional shape, each aperture may be formedwith a hexagonal shape like the sectional shape of the small lens.

The light from the optical integrator 19 goes by way of the lens 20, themirror 21, the lens 22 and the half mirror 23 to the blade device 24.Here, the light beams from the lenses of the integrator 19 aresuperposed one upon another on the plane of the blade device 24, wherebythe blade device 24 is illuminated with uniform illuminance. Also, thehalf mirror 23 serves to reflect a portion of each light beam from eachlens of the integrator 19, and the light blocking plate 40 isilluminated with the reflected light. Light passing through the apertureof the light blocking plate 40 is collected by the lens 41 on thequartered detector 42.

The light passing through the aperture of the blade device 24 isdirected by the mirror 25, the lens 26, the mirror 27 and the lens 28 tothe reticle 30. Since the aperture of the blade device 24 and thecircuit pattern of the reticle 30 are in an optically conjugaterelationship, the light beams from the lenses of the integrator 19 aresuperposed one upon another, also on the reticle 30. Thus, the reticle30 is illuminated with uniform illuminance, and an image of the circuitpattern of the reticle 30 is projected by the projection lens system 31.

The detector sections of the quartered detector 42 correspondrespectively to four separate portions of the effective light sourcesuch as shown in FIG. 3A, and each section is able to detect the lightquantity in each corresponding portion independently of the others. Bycombining the outputs of all the sections, the opening/closing controlfor the shutter 15 can be effected, as described hereinbefore. On theother hand, by mutually comparing the outputs of the sections, anyunbalance in proportion of the light quantities at the respectiveportions of the effective light source can be checked. Here, calibrationamong the detector sections of the quartered detector 42 is effectivefor enhanced reliability of the unbalance check. Such calibration willbe described later.

The shape of the effective light source formed on the pupil plane of theapparatus corresponds to the shape of the integrator 19. Since theintegrator 19 itself is provided by a combination of small lenses, in amicroscopic sense the light quantity distribution of the effective lightsource comprises a combination of discrete ones each corresponding tothe shape of each lens. However, in a macroscopic sense, a lightquantity distribution such as shown in FIG. 3A is provided.

In this embodiment, the light quantity monitor means (23 and 40-42) andthe measuring unit (35-37) are used to check the light quantitydistribution of the effective light source. To this end, the X-Y stage34 is moved to place the measuring unit (35-37) to a position just belowthe projection lens system 31. In this measuring unit, light emanatingfrom the illumination system and reaching the image plane of theprojection lens system 31 is directed through the aperture 35a of theglass plate 35 and the aperture of the casing 36 to the photoelectricconverter 37. The light receiving plane of the aperture 35a is placed atthe image plane position of the projection lens system 31. The glassplate 35 is attached to the casing 36 and, as described, the casing 36has an aperture at a center thereof. In this example, the measuring unitis so arranged that the aperture of the casing 36 is displaceable to theaperture of the glass plate 35 by a predetermined amount whenillumination is provided with the illumination system of thisembodiment, on the top of the casing 36 four portions of an effectivelight source such as shown in FIG. 3A are provided. The size and shapeof the aperture of the casing 36 can be changed, as the aperture of theblade device 24. By changing the size and/or the shape of the apertureby means of a driving system (not shown), it is possible to detect eachof the four portions of the effective light source independently of theothers or, alternatively, it is possible to detect the four portions ofthe effective light source at once. On the other hand, the photoelectricconverter 37 has a light receiving portion of an area sufficient toreceive all the light passing through the aperture 35a of the glassplate 35. If the area of the light receiving portion of thephotoelectric converter 37 is too large and the response characteristicof the electrical system degrades, a condensing lens may be insertedbetween the glass plate 35 and the photoelectric converter 37 to collectthe light from the aperture 35a of the glass plate 35. This is effectiveto reduce the area of the light receiving portion of the photoelectricconverter 37 to thereby improve the response characteristic. Further, ifdesired, the uniformness of the illuminance on the image plane can bemeasured by moving the X-Y stage 34 along the image plane while holdingthe aperture of the casing 36 in a state for concurrent detection of allthe four portions of the effective light source.

The result of measurement of the light quantity (intensity) in eachportion of the effective light source obtained through cooperation ofthe movement of the casing 36, is compared with an output of acorresponding one of the detector sections of the quartered detector 42at the illumination system side. Namely, the photoelectric converter 37at the X-Y stage 34 side is used as a reference detector for calibrationof the output of the quartered detector 42. This allows stablemonitoring of any change with time of the effective light source. Then,any unbalance in light quantity of the portions of the effective lightsource can be detected by means of the quartered detector 42 or thephotoelectric converter 37, and light quantity matching of the portionsof the effective light source can be done by using the filters 17a-17d.

In this embodiment: through the function of the stop member 18 shown inFIG. 6B, an effective light source not having any peak of light quantitydistribution on the x or y axis, corresponding to the directions of thelongitudinal and lateral pattern features of the reticle 30, or at thepupil center (optical axis), is defined by zero-th order light on thepupil plane of the protection lens system 31, while on the other hand,by means of the illumination system (11, 12, 13, 14, 15, 16, 17, 18, 19,20, 21, 22, 23, 24, 25, 26, 27 and 28), the circuit pattern of thereticle 30 is illuminated with uniform illuminance. Thus, an image ofthe circuit pattern is projected by the projection lens system 31 uponthe wafer 32, whereby the image of the circuit pattern is transferred tothe resist of the wafer 32. The effect of such projection exposure is ashas been described hereinbefore with reference to FIGS. 3 and 4 and,with the use of light of i-line, a fine pattern of 0.4 micron can berecorded on the resist of the wafer 32 sharply and stably.

FIG. 7 is a fragmentary schematic view of a fourth embodiment of thepresent invention, which is an improved form of the semiconductor devicemanufacturing projection exposure apparatus of FIG. 6. The elements ofFIG. 7 corresponding to the FIG. 6 embodiment are denoted by the samereference numerals as those of FIG. 6.

In the drawing, denoted at 11 is an ultra-high pressure Hg lamp, anddenoted at 12 is an elliptical mirror. In this example, light emanatingfrom the elliptical mirror 12 is divided by a combination of beamsplitters (51-53). More specifically, in order to provide an effectivelight source having four portions such as shown in FIG. 3A, the lightemanating from the elliptical mirror 12 is divided sequentially by meansof a first beam splitter 51 and a second beam splitter 53. Denoted at 52is a deflecting mirror for deflecting the light path. The second beamsplitter 53 is disposed obliquely across the light paths of the twolight beams as divided by the first beam splitter 51, and it serves todivide each of the two light beams advancing along the sheet of thedrawing and to deflect a portion of each of the two light beams in adirection perpendicular to the sheet of the drawing. The remainingportion of each of the two light beams, not deflected, goes along thesheet of the drawing, as illustrated. A mirror optical system (notshown) is disposed on the path of that portion of light as deflected bythe second beam splitter 53, and it serves to reflect and direct thatportion of light along a path parallel to the path of light notdeflected by the second beam splitter. In this manner, by means of thebeam splitters 51 and 53 and the mirror 52 as well as the unshown mirroroptical system, the light path is divided into four light paths. Theselight paths are then combined so as to form a secondary light sourcewith a light distribution such as shown in FIG. 3A, on the light exitsurface of the integrator 19. As a result, on the pupil plane of theprojection lens system 31, an effective light source such as shown inFIG. 3A is formed.

On the two divided light paths which are present on the sheet of thedrawing, relay lenses 61a and 62aare disposed, respectively. These relaylenses 61a and 62aserve to collect the light beams, advancing along therespective paths, on the integrator 19. Since the insertion of the firstbeam splitter causes a difference in optical path length between thesetwo light paths, the relay lenses 61a and 61b are slightly differentfrom each other with respect to the structure and the focal length. Thisis also the case with an additional pair of relay lenses (not shown)which are disposed on the pair of light paths, not shown in the drawing.

Denoted at 63 is a shutter which can be controlled (opened/closed) foreach of the four light beams provided by the beam splitters 51 and 53.Denoted at 16a and 16b are wavelength selecting filters disposed on thetwo divided light paths, respectively, which are present on the sheet ofthe drawing. While not shown in the drawing, similar filters aredisposed on the two light paths which are not on the sheet of thedrawing. These filters each serve to extract the i-line component out ofthe light from the Hg lamp, as the filter 16 of the precedingembodiment. Denoted at 17a, and 17b are filters disposed on the twodivided paths in the sheet of the drawing, each for adjusting the lightquantity in a corresponding portion of the effective light source.Similar filters are disposed on the two light paths not included in thesheet of the drawing. These filters have a similar function as those ofthe filters 17a-17d of the preceding embodiment.

In this embodiment, the light path to the integrator is divided intofour and, for this reason, the integrator is provided by a combinationof four small integrators. Because of the relationship of superpositionof the light paths, only two integrators 19a and 19b are illustrated inthe drawing. Since the structure after the integrators is similar tothat of the preceding embodiment, further description will be omittedfor simplicity.

FIG. 8 is a fragmentary schematic view of a fifth embodiment of thepresent invention, showing a semiconductor device manufacturingprojection exposure apparatus wherein an image of a fine pattern isprojected in accordance with a method of the present invention.

In the apparatus of this embodiment, the position of an effective lightsource is changed with time to thereby form an equivalent effectivelight source as of that shown in FIG. 3A is formed on the pupil plane,and the image of a circuit pattern is projected. In FIG. 8, the elementscorresponding to those of the preceding embodiments are denoted by thesame reference numerals. Thus, denoted at 11 is an ultra-high pressureHg lamp; denoted at 12 is an elliptical mirror; denoted at 14 is adeflecting mirror; denoted at 15 is a shutter: denoted at 16 is awavelength selecting filter; and denoted at 19 is an optical integrator.The unshown portion, after the projection lens system 31, has the samestructure as that of the preceding embodiments.

An important feature of this embodiment resides in that a flat parallelplate 71 which is movable with time is disposed after the integrator 19.The parallel plate 71 is disposed obliquely to the optical axis of theillumination optical system, and it is swingable to change the anglewith respect to the optical axis, as illustrated, to shift the opticalaxis. This means that, if the integrator 19 is observed through the flatparallel plate 71, from the reticle 30 side, the integrator 19 appearsto move up and down or left and right with the swinging movement of theparallel plate 71. In this example, the parallel plate 71 is sosupported that it can be moved also rotationally about the optical axis.Therefore, by rotationally moving the parallel plate 71 while retainingits inclination of at a predetermined angle to the optical axis, uponthe pupil plane of the projection lens system 31 it is possible to placea single effective light source at a desired position on a circumferenceof a certain radius, spaced from the optical axis (pupil center). Foractual exposure operation, the parallel plate 71 is moved and, when thesingle effective light source comes to a desired position, the attitudeof the parallel plate is fixed and the exposure is effected for apredetermined time period. Such operation is executed four times so asto provide a single light source at each of the four portions of theeffective light source as shown in FIG. 3A and, then, the exposure ofone shot area (of the wafer) is completed.

In this embodiment, the Hg lamp 11 is used as a light source. If a lightsource of pulse emission type such as an excimer laser is used, theparallel plate 71 may be moved uninterruptedly and the exposure controlmay be such that the light source is energized when the parallel plate71 comes to a predetermined position. In such a case, conveniently anexcimer laser is used as a light source and the period of rotation ofthe parallel plate 71 about the optical axis may be selected to bematched with the emission repetition frequency of the excimer laser. Asan example, if the laser used emits at 200 Hz, then efficient exposureis attainable by so controlling the number of revolutions of theparallel plate that the effective light source displaces to an adjacentquadrant in response to each light emission.

When the system is arranged so that a single effective light sourcedisplaces with time, the effective light source portions (distributions)as defined in different portions of the pupil are provided by the lightenergy from one and the same light source and, therefore, it is easy toset, at the same intensity, the effective light source portions to beseparately defined on the pupil plane. This is the very reason why thefilter 17, used in the preceding embodiments for correction of lightquantity of the effective light source, is not provided.

Referring back to the drawing, the light passing through the parallelplate 71 goes by way of a lens 72, a half mirror 73 and a lens 74, andit illuminates the reticle 30 uniformly. Since the first imaging opticalsystem used in the preceding embodiments is not used in this embodiment,a blade device 74 separate from the blade device 24 of the precedingembodiments is provided in the neighborhood of the reticle 30. The bladedevice 74 has a similar structure and a similar function as of those ofthe blade device 24, and the size of the aperture thereof can be changedin accordance with the size of the circuit pattern formed on the reticle30.

The mirror 73 serves to reflect almost all the portion of the lightinputted thereto, but it also serves to transmit and direct a portion ofthe input light to a light quantity monitor, provided for exposurecontrol. Denoted at 35 is a condenser lens, and denoted at 76 is apinhole plate which is disposed at a position optically equivalent tothat of the reticle 30. Light from the mirror 73 is collected by thecondenser lens 75 upon the pinhole plate 76, and light passing throughthe pinhole plate 76 is received by a photodetector 77. Thephotodetector 77 produces a signal corresponding to the intensity oflight impinging on it. On the basis of this signal, an unshown computerof the apparatus controls the opening/closing of the shutter 15. It isto be noted here that, since in this embodiment it is not necessary tomonitor the light quantity ratio of the portions of the effective lightsource, the photodetector 77 may be of a type other than a quartereddetector.

In this embodiment: while an effective light source such as shown inFIG. 3A is defined on the pupil plane of the projection lens system 31,the circuit pattern of the reticle is illuminated with uniformilluminance. Thus, an image of the circuit pattern is projected by theprojection lens system 31, whereby the image of the circuit pattern istransferred to the resist of the wafer. The effect of such projectionexposure is as has been described hereinbefore, and a fine pattern of0.4 micron can be recorded on the resist of the wafer 32 sharply andstably.

FIG. 9 is a fragmentary schematic view of a sixth embodiment of thepresent invention, showing a semiconductor device manufacturingprojection exposure apparatus wherein an image of a fine pattern isprojected in accordance with a method of the present invention.

In this embodiment, a KrF excimer laser 81 (center wavelength 248.4 nmand bandwidth 0.03-0.05 nm) is used as a light source. Importantfeatures reside in that: since the excimer laser 81 is of pulse emissiontype, no shutter is provided and the exposure control is done throughthe actuation control of the laser itself; and, since the laser itselfis equipped with a filter and the bandwidth of laser light is narrowed,no wavelength selecting filter is provided. The beam splitters 51 and53, the mirror 52, the filter 17 and the integrator 19 have a similarfunction as those of the embodiment shown in FIG. 7. The portion afterthe integrator 19 is of a similar structure as shown in FIG. 6A, exceptthat a projection lens system (not shown) is provided by a lens assemblydesigned with respect to a wavelength 248.4 run and consisting of silica(main component).

In the excimer laser 81, the laser light has high coherency and,therefore, it is necessary to suppress production of a speckle pattern.To this end, in this embodiment, an incoherency applying unit 82 isprovided at a position after the light is divided by the beam splittergroup (51-53). While many proposals have been made as to how to removethe speckle in an illumination optical system using an excimer laser,the provision of an effective light source in accordance with thepresent invention is essentially compatible to them, and various knownmethods may be used. In consideration of this, details of the unit 82are omitted here.

In this embodiment: while an effective light source such as shown inFIG. 3A is defined on the pupil plane of the projection lens system 31through the illustrated illumination optical system (17, 19, 51, 52, 53and 82), the circuit pattern of the reticle is illuminated with uniformilluminance. Thus, an image of the circuit pattern of is projected bythe projection lens system 31, whereby the image of the circuit patternis transferred to the resist of the wafer. The effect of such projectionexposure is as has been described hereinbefore, and a fine pattern of0.3-0.4 micron can be recorded on the resist of the wafer 32 sharply andstably.

FIG. 10 is a fragmentary schematic view of a seventh embodiment of thepresent invention, which is an improved form of the apparatus of thesixth embodiment shown in FIG. 9.

In this embodiment, laser light from a laser 81 is divided into fourlight beams by a reflection type pyramid-like prism. While in theapparatus of FIG. 6 a transmission type pyramid-like prism 13 is usedfor the light division, the same effect is attainable by using areflection type one. As a matter of course, the structure of this aspectof the present invention can be realized by using an ultra-high pressureHg lamp but, in this example, a KrF excimer laser is used as a lightsource. The laser light emanating from the laser 81 is transformed intoan appropriate beam diameter by means of an afocal beam converter 91and, after this, it enters a pyramid-like prism 92. The arrangement ofthe pyramid-like prism is so set that four reflection surfaces thereofare oriented to define, as a result, an effective light source such asshown in FIG. 3B, at the pupil position of the projection lens system(not shown). Denoted at 93 are mirrors for deflecting the lights asdivided and reflected by the reflection surfaces of the prism 92. Theportion after the mirrors 93 has a similar structure as that of theapparatus of FIG. 9, whereas the portion after the integrator 19 has asimilar structure as that of FIG. 6A, except the unshown projection lenssystem is provided by a lens assembly designed with respect to awavelength of 248.4 run and consisting of silica (main component).

Also in this embodiment: while an effective light source such as shownin FIG. 3A is defined on the pupil plane of the projection lens system31 through the illustrated illumination optical system (17, 19, 91, 92,93 and 82), the circuit pattern of the reticle is illuminated withuniform illuminance. Thus, an image of the circuit pattern is projectedby the projection lens system 31, whereby the image of the circuitpattern is transferred to the resist of the wafer. The effect of suchprojection exposure is as has been described hereinbefore, and a finepattern of 0.3-0.4 micron can be recorded on the resist of the wafer 32sharply and stably.

FIG. 11 is a fragmentary schematic view of an eighth embodiment of thepresent invention, showing another form of a semiconductor devicemanufacturing projection exposure apparatus wherein an image of a finepattern is projected in accordance with a method of the presentinvention.

In this embodiment, an illumination system using a bundle of fibers 101is shown. The fiber bundle 101 has a light entrance surface disposed ata position whereat light from an ultra-high pressure Hg lamp 11 isfocused by an elliptical mirror 12. Light beams are propagated throughthe fibers and are directed to the light entrance surfaces of theintegrators 19. The end portion of the fiber bundle remote from theultra-high pressure Mg lamp 11, that is, the end portion at the lightexit surface thereof, is branched into four bundles correspondingrespectively to the portions of the effective light source shown in FIG.3A. Filters 17 are disposed at the exits of the fiber bundles,respectively, for adjustment of light quantities in the portion of theeffective light source. The optical arrangement of the remaining portionof the apparatus is provided by the same structure as that of the FIG. 8embodiment. However, as a photodetector for the light quantitymonitoring, a quartered detector 102 is used to detect the balance oflight quantities from the fiber bundles (i.e. four portions of thesecondary light source and thus four portions of the effective lightsource). The detector sections of the quartered detector 102 correspondto the exits of the four integrators 19, respectively.

In this embodiment: while an effective light source such as shown inFIG. 3A is defined on the pupil plane of the projection lens system 31,the circuit pattern of the reticle is illuminated with uniformilluminance; and an image of the circuit pattern is projected by theprojection lens system 31, whereby the image of the circuit pattern istransferred to the resist of the wafer. The effect of such projectionexposure is as has been described hereinbefore, and a fine pattern of0.4 micron can be recorded on the resist of the wafer 32 sharply andstably.

FIG. 12 is a fragmentary schematic view of a ninth embodiment of thepresent invention, showing another example of a semiconductor devicemanufacturing projection exposure apparatus wherein an image of a finepattern is projected in accordance with a method of the presentinvention.

In this embodiment, an illumination system is provided by using aplurality of light sources. In this example, ultra-high pressure Hglamps 11a and 11b are used. However, it is a possible alternative to usean excimer laser and to construct a laser optical system, that is, anoptical system for a parallel beam of small divergence angle.

While not shown in the drawing because of superposition, four ultra-highpressure Hg lamps are used in this embodiment. Light beams from thesefour Hg lamps enter a concave lens 103. Then the light passes through awavelength selecting interference filter 16 and four filters, for theadjustment of light quantities in the portions of the effective lightsource, and is received by the integrators 19. The optical arrangementafter the integrators 19 is similar to that of the FIG. 11 apparatus,and an effective light source such as shown in FIG. 3A is formed on thepupil plane of the projection lens system 31. Thus, also in thisembodiment, an image of the circuit pattern of the reticle 31 isprojected on the wafer, whereby the image of the circuit pattern of thereticle is transferred to a resist of the wafer. The effect of suchprojection exposure is as has been described hereinbefore, and a finepattern of 0.4 micron can be recorded on the resist of the wafer,sharply and stably.

In the semiconductor device manufacturing projection exposure apparatushaving been described in the foregoing, the arrangement of the effectivelight source on the pupil plane is fixed. However, as described in theintroductory portion of the Specification, the parameter p representingthe center position of each portion of the effective light source andthe parameter q representing the radius of each portion or the radius ofa circle circumscribing it as well as the shape of each portion of theeffective light source are to be optimized in accordance with a circuitpattern which is the subject of the projection exposure. Inconsideration thereof, it is desirable to arrange the system so that ineach embodiment the parameters p end q, for example, are madechangeable. By way of an example, in an embodiment which uses the stopmember 18, a stop member having a variable aperture shape may be usedtherefor or, alternatively, different stop members having apertures ofdifferent shapes may be prepared.

Further, the apparatuses described hereinbefore are those for themanufacture of semiconductor devices. However, the invention is notlimited to the projection of an image of an integrated circuit pattern.That is, the invention is applicable to many cases wherein an image ofan article having a fine pattern mainly consisting of longitudinal andlateral pattern features, is to be projected through an optical system.

Further, while in the apparatuses described hereinbefore the imageprojecting optical system comprises a lens system, the invention isapplicable also to a case wherein a mirror system is used therefor.

Still further, while the apparatuses described hereinbefore use light ofi-line or laser light of wavelength 248.4 run for the image projection,the applicability of the present invention does not depend on thewavelength. Thus, as an example, the invention is applicable to asemiconductor device manufacturing projection exposure apparatus whichuses light of g-line (436 nm).

As described in the foregoing, through formation of a specific effectivelight source on a pupil of an image projection optical system, an imageof a fine pattern having a very high frequency can be protected with asimilar resolution as attainable with a phase shift mask and,conveniently, with a simple process as compared with the use of thephase shift mask.

As described, the present invention has paid a particular note to thenecessary resolution for and the directionality of a pattern of asemiconductor integrated circuit and proposes selection of an optimumillumination method, best suited to the spatial frequency and thedirectionality of that pattern.

Some embodiments to be described below have an important feature that:in order to meet the semiconductor integrated circuit manufacturingprocesses including steps of a maximum number not less than 20 (twenty),an illumination device has a conventional illumination system and ahigh-resolution illumination system which can be easily interchanged.

FIG. 13 is a schematic view of a main portion of an embodiment of thepresent invention. Denoted at 11 is a light source Such as an ultra-highpressure Hg lamp, for example, having its light emitting point disposedadjacent to a first focal point of an elliptical mirror 12. The lightemanating from the lamp 11 is collected by the elliptical mirror 12.Denoted at 14 is a mirror for deflecting the light path, and denoted at15 is a shutter for limiting the quantity of light passing therethrough.Denoted at 150 is a relay lens system which serves to collect the lightfrom the Hg lamp 11 on an optical integrator 19, through a wavelengthselecting filter 16. The optical integrator 19 is provided by smalllenses arrayed two-dimensionally, to be described later.

In this embodiment, the optical integrator 19 may be illuminated inaccordance with either a "critical illumination method" or a "Kohlerillumination method". Also, it may be that the light exit portion of theelliptical mirror is imaged on the optical integrator 19. The wavelengthselecting filter 16 serves to select and pass light of a necessarywavelength component or components (e.g. i-line or g-line), out of thewavelength components of the light from the Hg lamp 11.

Denoted at 12 is a stop shape adjusting member (selecting means forselecting intensity distribution of the secondary light source), foradjusting the shape of a stop, and it comprises a plurality of stopsprovided in a turret arrangement. The adjusting member is disposed afterthe optical integrator, more particularly, adjacent to the light exitsurface 19b of the integrator 19. The stop shape adjusting member 18serves to select predetermined ones of small lenses, constituting theoptical integrator 19, in accordance with the shape of the integrator19. Namely, in this embodiment, by using the stop shape adjusting member18, an illumination method suitable for the shape of a pattern of asemiconductor integrated circuit to be exposed (to be described later)is selected. Details of the selection of small lenses will be describedlater.

Denoted at 21 is a mirror for deflecting the light path, and denoted at122 is a lens system for collecting the light passing through theadjusting member 18. The lens system 122 plays an important role for thecontrol of uniformness of illumination. Denoted at 23 is a half mirrorfor dividing the light from the lens system 122 into a-transmitted lightand a reflected light. Of these lights, the light reflected by the halfmirror 23 is directed through a lens 138 and a pinhole plate 40 to aphotodetector 42. The pinhole plate 40 is disposed at a positionoptically equivalent to that of a reticle 30 having a pattern to beexposed (printed), and the light passing the pinhole plate is detectedby the photodetector 42 for the control of the amount of exposure (basedon control of the shutter 15).

Denoted at 24 is a masking mechanical blade device, and the positionthereof is adjusted by means of a driving system (not shown) inaccordance with the size of a pattern of the reticle 30, to be exposed.Denoted at 25 is a mirror, denoted at 26 is a lens system, denoted at 27is a mirror, and denoted at 28 is a lens system all of which serve toilluminate the reticle 30, placed on a reticle stage 137, with the lightfrom the Hg lamp.

Denoted at 31 is a projection optical system for projecting and imagingthe pattern of the reticle 30 upon a wafer 32. The wafer 32 is attractedto and held by a wafer chuck 33 and, also, it is placed on an X-Y stage34 whose position is controlled by means of a laser interferometer 136and an unshown controller. Denoted at 38 is a mirror mounted on the X-Ystage 34, for reflecting light from the laser interferometer.

In this embodiment, through the adjusting member 18, a secondary lightsource is formed at the light exit surface 19b side of the opticalintegrator 19, and the light exit surface of the integrator 19 isdisposed in an optically conjugate relationship with the pupil plane 31aof the projection optical system 31 through the elements 21, 122, 25,26, 27 and 28. Thus, an effective light source image corresponding tothe secondary light source is formed on the pupil plane 31a of theprojection optical system 31.

Referring now to FIG. 14, the relationship between the pupil plane 31aof the projection optical system 31 and the light exit surface 19b ofthe optical integrator 19 will be explained. The shape of the effectivelight source as formed on the pupil plane 31a of the projection opticalsystem 31 corresponds to the shape of the optical integrator 19. FIG. 14shows this, and in the drawing the shape of the effective light sourceimage 19c of the light exit surface 19b formed on the pupil plane 31a ofthe projection optical system 31 is illustrated superposedly. Forstandardization, the diameter of the pupil 31a of the projection opticalsystem is taken as 1.0 and, in this pupil 31a, the light exit surfacesof the small lenses constituting the optical integrator 19 are imaged toprovide the effective light source image 19c. In this embodiment, eachsmall lens of the optical integrator 19 has a square shape.

Here, the orthogonal axes which are the major directions to be used indesigning a pattern of a semiconductor integrated circuit, are taken onx and y axes. These directions correspond to the major directions of thepattern formed on the reticle 30, respectively, and also substantiallycorrespond to the directions (longitudinal and lateral sides) of theouter configuration of the reticle 30 having a square shape. Asdescribed and as is well known in the art, usually the orthogonal axesused in the pattern designing correspond to x and y axes defined in theprojection exposure apparatus with respect to which a reticle is to beplaced on the reticle stage. Also, the x and y axes correspond to x andy axes along which the X-Y stage 34 is moved.

The high-resolution illumination system shows its best performanceparticularly when the k₁ factor as described has a level near 0.5. Inconsideration of this, in this embodiment, through the restriction bythe adjusting member 18, only those light beams passing throughparticular ones of small lenses of the optical integrator 19, asselected in accordance with the shape of the pattern on the reticle 30surface, are used for the illumination of the reticle 30. Morespecifically, the selection of small lenses is so made as to assure thatthe light passes those regions of he pupil plane 31a of the projectionoptical system 31, other than the central region thereof.

FIGS. 15A and 15B are schematic views of the pupil plane 31a,respectively, each showing the result of selection of those light beamspassing particular ones of the small lenses of the optical integrator 19made by the restriction by the adjusting member 18. In each of thesedrawing, the painted area corresponds to the light blocking region whilethe non-painted areas correspond to the regions through which the lightpasses.

FIG. 15A shows an effective light source image on the pupil plane 31a tobe defined on an occasion when, for a pattern, the directions withrespect to which the resolution is required correspond to the x and yaxes, respectively. Assuming now that the circle representing the pupilplane 31a is expressed by:

    x.sup.2 +y.sup.2 =1,

the following four circles are considered:

    (x-1).sup.2 +y.sup.2 =1

    x.sup.2 +(y-1).sup.2 =1

    (x+1).sup.2 +y.sup.2 =1

    x.sup.2 +(y+1).sup.2 =1

By these four circles, the circle representing the pupil plane 31a isdivided into eight regions 101-108.

In this embodiment, an illumination system having high resolution andlarge depth of focus with respect to the x and y directions, can beassured by preferentially selecting a group of small lenses present ineven-numbered regions, namely, the regions 102, 104. 106 and 108, so asto pass the light through the selected small lenses. Thus, as anexample, a stop 18b or 18c illustrated in FIG. 16 is selected and theprojection exposure is effected. Those small lenses around the origin(x=0, y=0) have a large effect in enhancement of depth of focus chieflywith regard to a pattern of a relatively wide linewidth and, therefore,whether such small lenses are to be selected or not is a matter ofchoice which may be determined in accordance with a pattern to beprinted.

In the example of FIG. 15A, those small lenses around the center areexcluded and, thus, the formed effective light source is substantiallyequivalent to that shown in FIG. 3A. It is to be noted here that theoutside portion of the optical integrator 19 is blocked, against light,within the illumination system by means of an integrator holding means(not shown). Also, in FIGS. 15A and 15B; for better understanding of therelationship between the small lenses and the pupil plane 31a of theprojection optical system 31, the pupil plane 31a and the effectivelight source image 19c of the optical integrator 19 are illustratedsuperposedly.

FIG. 15B shows an example of restriction on an occasion when highresolution is required with regard to a pattern with features extendingin ±45 deg. directions. Like the case of FIG. 15A, the relationshipbetween the pupil 31a and the effective light source image 19c of theoptical integrator 19 is illustrated. For a ± pattern, under the samecondition, the following four circles may be drawn superposedly on thepupil 31a: ##EQU1## and, like the example of FIG. 15A, the pupil 31a isdivided into eight regions 111-118. On this occasion, those which arecontributable to the enhancement of the resolution of a pattern withfeatures of ±45 deg. are odd-numbered regions, that is, the regions 111,113, 115 and 117. By preferentially selecting those small lenses of theoptical integrator which are present in these regions, for the patternwith features of ±45 deg. and a k₁ factor of a level of about 0.5, thedepth of focus increases considerably. Thus, as an example, a stop 18dsuch as shown in FIG. 16 is selected and the projection exposure iseffected.

FIG. 16 is a schematic view of interchangeable stops 18a-18d of theadjusting member 18. As illustrated, a turret type interchangingstructure is used. The first stop 18a is used when a pattern which isnot very fine, as having a k₁ factor of not less than 1, is to beprinted. The first stop 18a has the same structure as in a conventionalillumination system known in the art, and which serves to block, againstlight, the outer portion of a small lens group of the optical integrator19. The stops 18a-18d are those added in accordance with the presentinvention.

Generally, in an illumination system for high resolution, anadvantageous result is obtainable to a high spatial frequency when aregion of the optical integrator which is, on the pupil plane, outsideof the size as required in the conventional type illumination system, isalso used. As an example, in the conventional type illumination systemit may be preferable to use those small lenses which are present withina radius of 0.5; whereas in an illumination system for high resolution,although small lenses around the center are not used, there is a casewherein those small lenses present within a circle of a maximum radiusof 0.75 on the pupil plane (the radius of the pupil plane is 1) shouldpreferably be used.

For this reason, the size of the optical integrator 19 as well as theeffective diameter of the illumination system, for example, should bepreferably determined while taking into account both the conventionaltype and the high-resolution type. Also, it is preferable that the lightintensity distribution at the light entrance surface 19a of the opticalintegrator 19 has a sufficient size such that it functions sufficientlyeven if a stop 18 is inserted. The possibility of blocking the outersmall lenses with the stop 18a is because of the reason described above.Thus, as an example, there may be a case wherein, although at theoptical integrator 19 side a maximum radius 0.75 is prepared, the stop18a chooses regions within a radius of 0.5.

By determining the shape of a stop in consideration of thespecifications of a pattern of a semiconductor integrated circuit to beprinted, as described, it is possible to arrange the exposure apparatusbest suited for that pattern. The selection of stops may be madeautomatically in response to a signal applied from a computer, providedfor overall control of the exposure apparatus. Illustrated in FIG. 16 isan example of stop shape adjusting member 18 formed with such stops. Inthis example, any one of four stops 18a-18d can be selected. As a matterof course, the number of stops may be increased easily.

There is a case wherein the non-uniformness in illumination changes withthe selection of a stop. In consideration of this, in this embodiment,such non-uniformness in illuminance can be finely adjusted by adjustingthe lens system 122. Such fine adjustment can be done by adjusting thespacing between constituent lenses of the lens system 122 in thedirection of she optical axis. Denoted at 151 is a driving mechanism fordisplacing one or more constituent lenses of the lens system 122. Theadjustment of the lens system 122 may be effected in accordance with theselection of the stop. If desired, the lens system 122 as a whole may bereplaced by another, in response to the change of the stop shape. Onthat occasion, different lens systems each corresponding to the lenssystem 122 may be prepared and, in a turret fashion, they may beinterchanged in accordance with the selection of the stop shape.

In this embodiment, as described, the shape of the stop is changed so asto select an illumination system suited to the characteristics of thepattern of a semiconductor integrated circuit. Also, an importantfeature of this embodiment resides in that, when an illumination systemfor high resolution is set, in general form of the effective lightsource, the light source itself is divided into four regions. Animportant factor in this case is the balance of intensity in these fourregions. However, in the arrangement shown in FIG. 13, there is a casewherein the shadow of a cable to the Hg lamp 11 adversely affects thisbalance. Therefore, in an illumination system for high resolutionwherein the stop means shown in FIG. 15A or 15B is used, it is desirableto set the arrangement so that the linear zone corresponding to theshadow of the cable coincides with those small lenses of the opticalintegrator which are blocked against light.

More specifically, in the FIG. 15A example, preferably the cable 11ashould be extended in the x or y directions, such as shown in FIG. 17A.In the FIG. 15B example, on the other hand, preferably the cable 11ashould be extended at an angle of ±45 deg. with respect to the x and ydirections. In this embodiment, preferably the direction of extension ofthe cable of the Hg lamp may be changed in response to the change of thestop.

FIG. 18 is a schematic view of a main portion of another embodiment ofthe present invention. The system of FIG. 18 is the same as that of FIG.13 with respect to the projection exposure of a pattern which is notvery fine, as having a k₁ factor not less than 1. On the hand, for theprojection exposure of a fine pattern with a k₁ factor about 0.5, a stopsuch as shown in FIG. 15A or 15B is inserted in accordance with thedirectionality of the pattern, as described in the foregoing. In thiscase, however, since the system of FIG. 13 simply blocks the light, theefficiency of the use of the light from the Hg lamp 11 decreases. Inconsideration of this, the embodiment of FIG. 18 arranged to assureeffective use of light.

To this end, in the system of FIG. 18, as am important feature apyramid-like prism 61 can be inserted between the elliptical mirror 12and the mirror 14. The light beam produced from a portion near anelectrode of the ultra-high pressure Hg lamp 11 is reflected by theelliptical mirror 12, and then it enters the pyramid-like prism 61whereby four light source images, corresponding to the four surfacesconstituting the prism, are formed on a plane including a second focalpoint of the elliptical mirror 12. Lens system 162 can be inserted inplace of the lens system 150, to direct the light so that the four lightsource images correspond respectively to four separate lighttransmitting portions of an inserted stop.

In this embodiment, the pyramid-like prism to be inserted should beplaced with specific orientation. For a stop of a shape such as shown inFIG. 15A, each ridge between adjacent surfaces of the prism 61 should beplaced in alignment with the x or y direction (FIG. 19A). For correctionof a change in the imaging relationship of the optical system due to theinsertion of the prism, in the system of FIG. 18 the lens system 150disposed after the shutter 15 is replaced by the lens system 162simultaneously with the insertion of the prism.

On the other hand, in a case when the light transmitting regions of thestop are on the x and y axes, as in the FIG. 15B example, each ridge ofprism is set with angles of ±45 deg. with respect to the x and y axes(FIG. 19B). Also in this case, lens 162 is used in place of the lenssystem 150 for the correction of the imaging relationship.

A plurality of pyramid-like prisms may be prepared in accordance withthe number of stops prepared.

FIG. 20 is a schematic view of a main portion of a further embodiment ofthe present invention. This embodiment differs from the FIG. 13embodiment in the structure of a lens system 65, imaging on the opticalintegrator 19. In this embodiment, the lens system 65 forms an image ofthe light exit surface of the elliptical mirror 12 on the opticalintegrator 19. Here, a case wherein a stop Such as shown in FIG. 16 isused is considered. What is a problem on this occasion is that there isa difference in maximum effective diameter of light as required on theoptical integrator 19, between a case wherein the stop 18a forconventional illumination method as described is used and a case whereinone the stops 18b-18d for the high-resolution illumination system isused.

In this embodiment in consideration of this, the lens system 65 isprovided by a zoom optical system so as to meet the change in diameterof light. Since the diameter of light from the ultra-high pressure Hglamp 11 is determined definitely by the light exit portion of theelliptical mirror 12, use of the zoom optical system 65 of thisembodiment assures control of the light beam diameter in accordance withan illumination method used. Thus, the light utilization efficiency isimproved.

The controllability of the size or the intensity distribution of thelight on the optical integrator 19 is important, also in a case whereinthe lens system 150 of the FIG. 13 system forms, on the light entrancesurface 19a of the integrator 19, an image of the Hg lamp 11, not animage of the light exit portion of the elliptical mirror 12.

Thus, for the control of the light intensity distribution on theintegrator 19, the Hg lamp itself may be displaced along the opticalaxis so that it is defocused with respect to the light entrance surface19a of the optical integrator 19.

FIG. 21 is a schematic view of a main portion of a further embodiment ofthe present invention. An important feature of this embodiment residesin that, in order to assure uniform light intensity distribution on theoptical integrator as well as even weight of the small lenses, theoptical integrator is used in duplex. In the drawing, denoted at 171 isa lens system which corresponds to the lens system 150, denoted at 16 isa wavelength selecting filter, and denoted at 172 is a first opticalintegrator. In accordance with the function of an optical integrator,light beams emanating from the small lenses constituting the firstoptical integrator 172 and passing a relay lens 173, are superposed oneupon another on a second optical integrator 174. As a result of this, auniform illuminance distribution is provided on the light entrancesurface 174a of the second optical integrator 174.

If in the preceding embodiments a uniform illuminance distribution isnot provided on the optical integrator 19 (as an example, thedistribution is like a Gaussian distribution wherein the level at thecenter is high), it is necessary to finally determine the shape of thestop for the high-resolution illumination on the basis of experiments,for example. In the present embodiment, on the other hand, since theweight (the light quantity supplied therefrom) of the small lenses iseven, the contrast of image performance can be controlled easily.Further, in this embodiment, double optical integrators are used, it isnot necessary to pay a specific attention to the cable as described withreference to FIGS. 17A and 17B.

FIG. 22 is a schematic view of a main portion of a further embodiment ofpresent invention. In this embodiment, a fiber bundle 181 is provided infront of the optical integrator 19. In this example, the zone of theoptical integrator to be irradiated is controlled by means of a spacingadjusting mechanism 182 and a driving mechanism 183 therefor, foradjusting the spacing of adjacent end portions of the fiber bundle 181,as branched into four in order to provide a distribution for aconventional type illumination system, the spacing of the four fiberbundles 181a-181d is narrowed. In order to provide a distributioncorresponding to that shown in FIG. 15A, the spacing of the fiberbundles 181a-181d is widened by a predetermined amount. Such adjustmentis effected in accordance with a stop 18 used. In the latter case,rotation of the fiber bundles 181a-181d is also necessary.

In some examples described hereinbefore, one ultra-high pressure Hg lamphaving been frequently used is used. However, as a matter of course, thepresent invention is applicable also to a case where plural lightsources are used or, alternatively, an excimer laser is used as a lightsource. On an occasion wherein an illumination system uses an excimerlaser, it is possible that the position of the laser on the opticalintegrator is scanned with time. In that case, by changing the range ofscan in accordance with the type of a circuit pattern to be printed, aneffective light source (image) such as shown in FIG. 15 can be providedeasily.

Although it has not been explained with reference to these embodiments,in the high-resolution illumination system the balance of the fourportions generally divided by the stop is important. Since details ofmonitoring the distributions of the four portions of the effective lightsource or of the manner of correcting the distribution have beendescribed hereinbefore, description of them is omitted here.

Further, while in these embodiments of the present invention the stopmeans is inserted at a position after the optical integrator, it may bedisposed in front of the integrator. As an alternative, if in theillumination system there is a plane which is optically conjugate withthe optical integrator, the stop may be disposed on such plane.

In some embodiments of the present invention described hereinbefore, inaccordance with the fineness or the directionality, for example, of apattern on a reticle to be projected and exposed, an illumination systemsuited to that pattern is selected to thereby assure an optimum exposuremethod and apparatus of high resolution. Further, these embodiments ofthe present invention provide an advantage that: for exposure of apattern which is not very fine, a conventional illumination system canbe used as it is; whereas for exposure of a fine pattern, while using anillumination system which assures high resolution with a small loss oflight quantity, it is possible to obtain a large depth of focus.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An exposure apparatus for forming an image of afine pattern having linear features extending in orthogonal first andsecond directions, said apparatus comprising:an illumination opticalsystem for illuminating the pattern, said illumination optical systemcomprising means for forming a secondary light source having decreasedintensity portions at a center thereof and on first and second axesdefined to intersect with each other at the center and defined along thefirst and second directions, respectively; and a projection opticalsystem for projecting, on an image plane, an image of the patternilluminated with light from said secondary light source, wherein saidlight source comprises four sections having substantially the same lightintensity and being distributed in four quadrants defined by the centerand the first and second axes, wherein an image of said light source isprojected onto a pupil of said projection optical system, and wherein,on the assumption of a coordinate system defined by X and Y axesextending along the first and second directions and intersecting at acenter of the pupil, and that a radius of the pupil is 1, coordinates ofcenters of the four sections are (p, p), (-p, p), (-p, -p) and (p, -p),wherein 0.25<p<0.6.
 2. An apparatus according to claim 1, wherein eachof said sections has a radius q, and 0.15<q<0.3.
 3. An apparatusaccording to claim 1, wherein each of the intensities of the decreasedintensity portions is substantially zero.
 4. A projection exposureapparatus for projecting an image of a pattern of an original on aworkpiece, said apparatus comprising:an X-Y stage for supporting thereonthe workpiece and being movable along X and Y directions in an X-Ycoordinate system defined in said apparatus; means for forming asecondary light source having decreased intensity portions at a centerthereof and on first and second axes defined to intersect with eachother at the center and defined along the X and Y directions,respectively; a condensing optical system for illuminating the patternof the original with light from said secondary light source; and aprojection optical system for projecting on the workpiece an image ofthe pattern illuminated with the light from said secondary light source,wherein said secondary light source comprises four sections havingsubstantially the same light intensity and being distributed in fourquadrants defined by the center and the first and second axes, andwherein an image of the secondary light source is projected onto a pupilof said projection optical light intensity and being distributed in fourquadrants defined by the center and the first and second axes, whereinan image of the light source is projected onto a pupil of a projectionoptical system, and wherein, on the assumption of a coordinate systemdefined by X and Y axes extending along the first and second directionsand intersecting at a center of the pupil, and that a radius of thepupil is 1, coordinates of centers of the four sections are (p, p), (-p,p), (-p, -p) and (p, -p), wherein 0.25<p<0.6.
 5. An apparatus accordingto claim 4, wherein each of the sections has a radius q, and 0.15<q<0.3.6. An apparatus according to claim 4, wherein each of the intensities ofthe decreased intensity portions is substantially zero.
 7. A projectionexposure apparatus for projecting an image of a pattern of an originalonto a workpiece, said apparatus comprising:an X-Y stage for supportingthereon the workpiece and being movable along X and Y directions in anX-Y coordinate system defined in said apparatus; means for forming alight source having an intensity distribution such that the portions ata center thereof and on first and second axes defined to intersect witheach other at the center and defined along the X and Y directions,respectively, are decreased in comparison with the portions of saidlight source other than said center portion and the portions along thefirst and second axes; a condensing optical system for illuminating thepattern of the original with light from said light source; and aprojection optical system for projecting on the workpiece an image ofthe pattern illuminated with the light from said light source, whereinsaid light source comprises four sections having substantially the samelight intensity and being distributed in four quadrants defined by thecenter and the first and second axes, and wherein an image of said lightsource is projected onto a pupil of said projection optical system, andwherein, on the assumption of a coordinate system defined by X and Yaxes extending along the first and second directions and intersecting ata center of the pupil, and that a radius of the pupil is 1, coordinatesof centers of the four sections are (p, p), (-p, p), (-p, -p) and (p,-p), wherein 0.25<p<0.6.
 8. An apparatus according to claim 7, whereineach of the sections has a radius q, and 0.15<q<0.3.
 9. An apparatusaccording to claim 7, wherein the intensities of the center portion andthe portions along the first and second axes are zero.
 10. An apparatusaccording to claim 7, wherein said light source forming means comprises(i) an optical integrator having a light receiving surface and a lightemitting surface, for receiving with said light receiving surface lightfrom a primary light source and dividing the received light to provide aplurality of light beams from said light emitting surface, and (ii) stopmeans having four apertures disposed adjacent to one of said lightreceiving surface and said light emitting surface of said opticalintegrator to define the four sections of said light source.
 11. Anapparatus according to claim 7, wherein said light source forming meanscomprises (i) an optical integrator having a light receiving surface anda light emitting surface, for receiving with said light receivingsurface light from a primary light source and dividing the receivedlight to provide a plurality of light beams from said light emittingsurface, and (ii) stop means for cross-like shape disposed adjacent toone of said light receiving surface and said light emitting surface ofsaid optical integrator to define the four sections of said lightsource.
 12. An apparatus according to claim 7, further comprising meansfor detecting the intensities in said four sections, and a member foradjusting a ratio of the intensities of said four sections.
 13. Anapparatus according to claim 12, wherein said intensity detecting meanscomprises a first intensity distribution sensor mounted to saidillumination optical system.
 14. An apparatus according to claim 13,wherein said intensity detecting means comprises a second intensitydistribution sensor adjacent the image plane of said projection opticalsystem, wherein the intensities of said four sections are detected bysaid first and second intensity distribution sensors, and a result ofsensing of said second intensity distribution sensor is corrected on thebasis of said sensing of said second intensity distribution sensor. 15.An apparatus according to claim 12, wherein said intensity detectingmeans comprises a second intensity distribution sensor disposed adjacentthe image plane of said projection optical system.
 16. An apparatusaccording to claim 7, wherein said light source forming means comprisesa lamp, an elliptical mirror for reflecting light from the lamp and anoptical integrator illuminated by the light reflected by said ellipticalmirror.
 17. An apparatus according to claim 7, wherein said light sourceforming means comprises a primary light source and a first opticalintegrator illuminated by light from said primary light source, and asecond optical integrator illuminated by light from said first opticalintegrator.
 18. An apparatus according to claim 7, wherein said lightsource forming means comprises a first light source, light splittingmeans for splitting light from said first light source into four beams,and an optical integrator illuminated by the four beams.
 19. Anapparatus according to claim 18, wherein said light splitting meanscomprise a bundle of fibers integrated at a side receiving the light anddivided at a side from which the light emits.
 20. An apparatus accordingto claim 18, wherein said light splitting means comprises apyramid-shaped prism.
 21. An apparatus according to claim 18, whereinsaid primary light source is a laser, and said light splitting meanscomprises means for making the four beams incoherent.
 22. An apparatusaccording to claim 21, wherein said laser is an excimer laser.
 23. Anapparatus according to claim 18, wherein said optical integrator hasfour separately disposed from each other.
 24. An apparatus according toclaim 7, wherein said light source forming means forms the four sectionssequentially.
 25. An apparatus according to claim 7, wherein said lightsource forming means comprises a plurality of primary light sources andan optical integrator illuminated by beams from the primary lightsources.
 26. An apparatus according to claim 25, wherein said lightsource forming means comprises four primary light sources.
 27. Anapparatus according to claim 25, wherein said optical integrator hasfour sections separately disposed from each other.
 28. An apparatusaccording to claim 7, wherein said light source forming means comprisesan optical integrator including an array of lenses and an aperture stopdisposed adjacent the optical integrator and having four aperturescorresponding to four sections of the light source, and wherein an edgeof the aperture extends along a cross section of the lens of said lensarray.
 29. An apparatus according to claim 7, wherein said light sourceforming means comprises means for switching the light source having thefour sections to another light source having an intensity distributiondifferent from that of said light source.
 30. An apparatus according toclaim 29, wherein said light source forming means comprises a mechanismfor selectively inserting across the optical path first and secondaperture stops having openings corresponding to the intensitydistributions of the light sources.
 31. An apparatus according to claim30, wherein said light source forming means comprises an opticalintegrator including an array of lenses, and said first and secondaperture stops are inserted across the optical path adjacent the opticalintegrator, and the edges of the first and second apertures are extendedalong a lens cross section of the lens array.
 32. An apparatus accordingto claim 30, wherein said light source forming means comprises a primarylight source and a zoom lens illuminating an optical integrator withlight from said primary light source, and wherein said first and secondaperture stops are inserted across the optical path adjacent the opticalintegrator.
 33. An apparatus according to claim 30, wherein said lightsource forming means comprises a primary light source and a pyramid-likeprism, insertable across the optical path, for splitting light from saidprimary light source into four beams.
 34. An apparatus according toclaim 33, wherein said light source forming means comprises two lenssystems inserted across the optical path alternately in interrelationwith the pyramid-shaped prism.
 35. An apparatus according to claim 30,wherein said light source forming means comprises a primary lightsource, and light splitting means for splitting light from said firstlight source into four beams, and said light splitting means comprisesfour fiber bundles which are united at a light receiving side, andseparated at a light emitting side.
 36. An apparatus according to claim30, further comprising means for correcting illuminance non-uniformityoccurring when the light source having four sections is switched toanother light source having a different intensity distribution.
 37. Anapparatus according to claim 36, wherein said correcting means comprisesa lens movable along the optical path.
 38. An apparatus according toclaim 37, wherein said light source forming means comprises a primarylight source, an optical integrator illuminated by light from saidprimary light source, and said movable lens in an optical path of thelight from the optical integrator.
 39. An apparatus according to claim29, wherein said light source forming means comprises an opticalintegrator including an array of lenses, and said first and secondaperture stops are inserted across the optical path adjacent the opticalintegrator, and the edges of the first and second apertures are extendedalong a lens cross section of the lens array.
 40. An apparatus accordingto claim 29, wherein said light source forming means comprises a primarylight source and a zoom lens illuminating an optical integrator withlight from said primary light source, and wherein said first and secondaperture stops are inserted across the optical path adjacent the opticalintegrator.
 41. An apparatus according to claim 29, wherein said lightsource forming means comprises a primary light source and a pyramid-likeprism, insertable across the optical path, for splitting light from saidprimary light source into four beams.
 42. An apparatus according toclaim 41, wherein said light source forming means comprises two lenssystems inserted across the optical path alternately in interrelationwith the pyramid-shaped prism.
 43. An apparatus according to claim 29,wherein said light source forming means comprises a primary lightsource, and light splitting means for splitting light from said firstlight source into four beams, and said light splitting means comprisesfour fiber bundles which are united at a light receiving side, andseparated at a light emitting side.
 44. An apparatus according to claim29, further comprising means for correcting illuminance non-uniformityoccurring when the light source having four sections is switched toanother light source having a different intensity distribution.
 45. Anapparatus according to claim 44, wherein said correcting means comprisesa lens movable along the optical path.
 46. An apparatus according toclaim 45, wherein said light source forming means comprises a primarylight source, an optical integrator illuminated by light from saidprimary light source, and said movable lens in an optical path of thelight from the optical integrator.
 47. A device manufacturing methodcomprising a step of printing a device pattern on a substrate, using anexposure apparatus as defined in any one of the claims 1 through
 6. 48.A method of forming an image of a fine pattern having linear featuresextending in orthogonal first and second directions, said methodcomprising the steps of:illuminating the pattern with light from a lightsource, said light source having an intensity distribution such that theportions at a center thereof and on first and second axes defined tointersect with each other at the center and defined along the first andsecond directions, respectively, are decreased in comparison withportions of the light source other than the center portion and theportions along the first and second axes, wherein said light sourcecomprises four sections having substantially the same apertures disposedadjacent to one of said light receiving surface and said light emittingsurface of said optical integrator to define the four sections of saidlight source.
 49. A method according to claim 48, wherein each of thesections has a radius q, and 0.15<q<0.3.
 50. A method according to claim48, wherein the intensities of the center portion and the portions alongthe first and second axes are zero.
 51. A method according to claim 48,wherein said light source forming means comprises (i) an opticalintegrator having a light receiving surface and a light emittingsurface, for receiving with said light receiving surface light from aprimary light source and dividing the received light to provide aplurality of light beams from said light emitting surface, and (ii) stopmeans having four system, and wherein, on the assumption of a coordinatesystem defined by X and Y axes extending along the first and seconddirections and intersecting at a center of the pupil, and that a radiusof the pupil is 1, coordinates of centers of the four sections are (p,p), (-p, p), (-p, -p) and (p, -p), wherein 0.25<p<0.6.
 52. A methodaccording to claim 48, wherein said light source forming means comprises(i) an optical integrator having a light receiving surface and a lightemitting surface, for receiving with said light receiving surface lightfrom a primary light source and dividing the received light to provide aplurality of light beams from said light emitting surface, and (ii) stopmeans for cross-like shape disposed adjacent to one of said lightreceiving surface and said light emitting surface of said opticalintegrator to define the four sections of said light source.
 53. Amicrodevice manufacturing method comprising a step of printing a devicepattern on a workpiece using an apparatus as defined in any one ofclaims 7 through
 46. 54. A microdevice provided by printing a devicepattern on a workpiece using an apparatus as defined in any one ofclaims 7 through 46.